Protective system



s. WIDMER 'PROTECTIVE SYSTEM Filed March 22, 1933 Aprilso, 1935 Patented Apr. 30, 1935 UNITED STATES PATENT OFFICE PROTECTIVE SYSTEM Stefan Widmer, Baden, Switzerland, assignor to Aktiengesellschaft Brown Boveri & Cie., Baden, Switzerland, a joint-stock company of Switzerland Application March22, 1933, Serial No. 662,155

In Germany March 26, 1932 3 Claims. (01. 175363) This invention relates to improvements in protective systems for electron discharge devices,

one anode to another.

means are. provided whereby the control electrodes are brought to and maintained at negative potentials with respect to the potential of a cathode of the device, thereby preventing the transfer of the discharge within the device from The flow of current is then. confined to a single anode and is then inor even destroy the electron discharge device and the associated equipment. If the device is utilized to supply the plate circuit of radio transmitting tubes, momentary breakdown of the impedance of a tube may permitthefiow of an excessive current which will cause destruction of the tube unless such currentis interrupted within a sufflciently short time. If the output circuit of the device is inductive, the inductance thereof tends to maintain the flow of current therethrough for a considerable length of time even when the source tends to make the anode negative with respect to the cathode of the device, such, result being due to the additional electromotive forces introduced in the circuit by the flow of current through the inductive portions thereof. To obtain a rapid interruption of the flow of current, it is then necessary to neutralize the effect of such inductance by bridging the inductive members, withsuitable impedance means which prevent the inductance from further acting on the flow of current in the circuit.

It is, therefore, among the objects of the pres:

ent invention to provide a protective system for electron discharge devices supplying circuits containinginductive members in which system the current flowing through the device isinterrupted within a minimum length of time upon occurrence of an overload or of a short circuit in the output circuit. 7

Another object of the invention is to provide a protective system for electron discharge devices r supplying circuitscontaining inductive members in which system the current flowing through the device is caused to be interrupted by negatively energizing the control electrodes of the device with respect to the cathode potential.

Another object of the invention is to provide a protectivesystem for electron discharge devices supplying circuits containing inductive members in which system the current in the device is interrupted within a minimum length of time irrespective of the presence of the inductive members in the output circuit. 1 v Another object of the invention is to provide a protective system for electron discharge devices supplying circuits containing inductive members in which such members are shunted by resistance means upon occurrence of an overload or of: a shortcircuit in the output circuit.

Another object of the invention is to provide a protective system for electron discharge devices supplying circuits containing inductive members in which such members are shunted by a condenser upon occurrence of an overload or of a short circuit in the output circuit. 7

Another object 'of the invention is to provide. a protective system forelectron discharge devices supplying circuits'containing inductive members in which the current in the-device is interrupted when such inductive members receive substantially the entire output voltage of the device..,,

Objects and advantages, other than those above described, will be apparent from the following description when read in connection with the, accompanying drawing, in which:

Fig. 1 diagrammatically illustrates one em-. bodiment of the present invention in which an electron discharge device is operable as an alterhating current rectifier supplying current to an I differing .irom that illustrated in Fig. l in that r the reactor may be bridged by a condenser charged from the output line; and. I

Fig. 3 is a'diagram of the output voltage and output current of the device upon occurrence of an overload or a short circuit in the output circuit.

Referring more particularly to the drawing by characters of reference, reference numeral 6 designates an alternating current supply line of any desired frequency and number of phases, herein shown as a three phase line only for the reason that such type of line is most frequently utilized in practice. Line 6 is connected with the electron discharge device I3 preferably over a transformer having a primary winding 8 and a secondary winding 9 comprising a plurality of phase portions connected in star to form a neutral point I0. The connection between line 6 and winding 8 may be controlled by means of a circuit breaker I operable by any suitable known means in response to any conditions of the system. The difierent phase portions of winding 9, such as 911, are severally connected with the anodes, such as II, of the electron discharge device I3 having control electrodes such as I2 associated with the anodes and having a cathode I4. It will be assumed that cathode I 4 is connected with the positive conductor IT or" the direct current output circuit over a reactor IS. The negative conductor I8 of the output circuit is con nected with neutral point !D of transformer secondary winding 9. A condenser I9 is connected between conductor I! and I8 for the purpose of cooperating with reactor I6 to smooth the wave of the output current and voltage. Diu'ing normal operation of device I3, the control electrodes are preferably maintained at a positive potential with respect to the potential or" cathode I 4, by means of a battery 2|, each control electrode being connected with the battery over a resistance, as at 22, and over the contacts of a relay 23. Relay 23 is operable to reverse the connections of battery 2| upon energization of the coil 24 thereof. Reactor I6 may be bridged by a resistance 25 of suitable value and current carrying capacity over thecontacts of a relay 21 having an operating coil 28. Coils 24 and 28 receive current upon breakdown of a spark gap 30 connected in series therewith, the flow of such current being limited by resistance 26 and a suitable additional resistance 29. Coils 24 and 28 are also bridged by a protective resistance 3| for the purpose of diverting any dangerous voltage surges which may be impressed on the coils.

In operation, the system being connected as shown and line 5 being energized, upon closure of circuit breaker winding 8 receives current from line 6 and induces voltages in the several portions of winding 9; the anodes of device I3 are thereby sequentially energized and sequentially carry currents which combine at cathode I4 to form a direct current flowing over reactor I6, conductor I I, the load circuit (not shown) and conductor I8 back to winding 9. The direct current voltage and the direct current present ripp les of predetermined frequencies which are re duced to any desired extent by suitable choice of reactor I6 and condenser I9. Upon occurrence of a short circuit in line IT, I8, the condenser IS discharges through such short circuit and has no further action so that conductor I! may be considered as directly connected with neutral point iii of transformer secondary winding 9. The entire output voltage of device !3 is thus impressed across reactor I6 which limits the flow of output current. Such full output voltage is also impressed across spark gap which is adjusted to break down at such voltage, thereby permitting flow of current over relay coils 24 and 28, resistance 29 and resistance 26. Relays 23 and 21 are so adjusted that relay 23 operates first to reverse the connections of battery 2| with cathode I4 and the control electrodes of device I3 thereby impressing a potential negative relative to cathode potential on the control electrodes. Assuming that, at the instant considered, anode II is carrying current, the discharge will not be able to transfer to another anode because of a negative energization of the control electrodes, so that anode II continues to carry current alone as is well known. Control electrode I2 is then without action on the flow of such current.

Referring to Fig. 3, curve 32 represents the voltage of cathode I4 with respect to point III, the curve of such voltage being formed by portions of the phase output voltages of winding 9 minus the arc drop within device I3. represents the direct current which has a wave shape similar to that of curve 32. Assuming that a short circuit in line H, I8 occurs at a time represented by point A, the output voltage of device I3 which is then impressed across reactor I5 remains substantially as represented by curve 32. The current, however, begins to increase to a considerably higher value. Assuming that relay 23 reverses the connections of battery 21 at a time corresponding to point B, and assuming that anode I I is carrying current, the output voltage of device I3 is then represented by a sine curve 34 which is substantially the voltage curve of transformer secondary winding portion 9a.

The successive half wave portions of curve 34 are alternately positive and negative, but the action of reactor I6 maintains a continuous flow of current through device I3 over a period of time comprising a large number of cycles of the voltage of line 6 by always maintaining cathode I4 negative with respect to anode I I so that current may continuously flow through device I3. Such current is then represented by curve 36 in Fig. 3 and generally comprises an alternating component to which is added a decreasing direct component due to the slow dissipation of the magnetic energy stored in reactor I6. Relay 21 is so adjusted as to close at a time represented by point C which is approximately the time at which curve 34 passes through zero. pressed on anode I I by transformer winding portion 9a is then zero and the current represented by the curve 36 is momentarily at a substantially constant value. Reactor I6 then being bridged by resistance 26, the greater portion of such current is transferred to resistance 26 and the magnetic energy stored in reactor I5, which caused the current flowing therethrough to be unidirectional, is rapidly dissipated in resistance 26 by the flow of a rapidly increasing current. The flow of current thereafter tends to become alternating, and the voltage of winding portion So then being substantially zero or even negative, the flow of current through device I3, which flow cannot reverse, is no longer sustained by such voltage and ceases within a very short period of time, at a time such as the time corresponding to point D. Due to the negative energization of the control electrodes of device I3, the flow of current continues to be interrupted until relay 23 returns to the position shown. By selecting point C near the passage of curve 34 through zero, the flow of current is interrupted without production of surges and without unduly burdening the resistance 26 but the value of resistance 26 must be such Curve 33 The voltage imthat the flow of current ceases before the voltage of transformer winding portion 9a reaches the lowest negative value thereof at pointE as the continuation of the flow of current beyond such point would permit such current to increase again due to the rising voltage of winding portion 9a and device l3, such action being again substantially neutralized by the connection of resistance 26 as above described. a

In the embodiment illustrated in Fig. 2 resistance 26 is replaced by a condenser 31 connected between cathode l4 and conductor l8 by a high resistance 38. Such resistance permits the slow charge or discharge of condenser 31 but doesnot provide a path for a rapid discharge thereof, similar to the discharge of condenser I 9, upon occurrence of a short circuit in lines l1, [8. When condenser 31 is connected in parallel with resistance l6 over the contacts of relay 21, such condenser and such reactor constitute a resonant circuit in which voltage surges may reach a high value. Such voltage surges may be dissipated over a spark gap 4| and a resistance 39.

The operation of the present embodiment is similar tothat of the embodiment illustrated in Fig. 1. Upon occurrence of a short circuit in line H, I8, spark gap 30 breaks down, thereby causing relays 23 and 21 to operate in the above set forth sequence. Condenser 31 being charged at'the' normalvoltage of line l1, l8 and being connected between the cathode l4 and point I0 of transformer winding 9 over the short circuit, the condenser tends to maintain cathode It at the normal voltage thereof with respect to point II) as represented by curve 32. When the voltage impressed on anode II from windingportion 9a decreases below the normal value, the flow of current between anode H and cathode l4 ceases and is not reestablished because of the negative energization of the control .electrodes of all anodes as above described. Such current interruption is slightly delayed because, while the voltage of anode I8 is decreasing, condenser 31 is discharging over reactor l 6 to neutralize the magnetic energy By a suitable choice of stored in the reactor. the condenser 31 the discharge of such condenser leaves the voltage thereof at a value suflicient to permit interruption ofthe current in device I3 before the time represented by point D.

Although but a few embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art thatvarious changes and modifications may be made therein without departing from the spirit of the invention or from the scope of. the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In combination, a supply line, an electron discharge device connected with said line, an output line connected with said device, inductive means in said output line, impedance means connected with said output line, means for causing I interruption of the fiow of current through said device, means for bridging said inductive means .with said impedance means, and means responsive to abnormal conditions in said output line to cause sequential operation of the third and fourth said means.

2. In combination, a supply line, a transformer connected with said line, an electron discharge device connected with said transformer, an output line connected with said transformer and 3. In combination, a supply line, a transformer connected with said line, an electron discharge device connected with said transformer, an output line connected with said transformer and with said device, inductive means in said output line, impedance means connected with said output line, means for causing interruption of the flow of current through said device, means for bridging said inductive means with said impedance means, and means responsive to the magnitude of the flow of current in said output line to cause sequential' operation of the third and fourth said means.

4. In combination, a supply line, a transformer connected with said line, an electron discharge device connected with said transformer, an outmeans to cause operation of. the third and fourth said means.

5. In combination, a supply line, a transformer connected with said line, an electron discharge .device connected with said transformer and having anodes with associated control electrodes and a cathode, an output line connected with said transformer and with said device, means for rendering said control electrodes negative with respect to said cathode, inductive means in said output line, impedance means connected with said output line, means for bridging said inductive means with said impedance means, and

means responsive to abnormal conditions in said output line to cause sequential operation of the third and fourth said means.

6. In combination, a supply line, a transformer connected with said line, an electron discharge device connected with said transformer and having anodes with associated control electrodes and a cathode, an output line connected Cal with said transformer and with said device, means for rendering said control electrodes negative with respect to said cathode, inductive means in said output line, resistance means connected with said output line, means for bridging said inductive means with said impedance means, and means responsive to abnormal conditions in said output line to cause sequential operation of the third and fourth said means.

'7. In combination, a supply line, a transformer connected with said line, an electron discharge device connected with said transformer and having anodes with associated control electrodes and a cathode. an output line connected with said transformer and with said device, means for rendering said control electrodes negative with respect to said cathode, inductive means in said output line, condenser means connected with said output line, means for bridging said inductive means with said condenser means, and means responsive to abnormal conditions in said output line to cause operation of the third and fourth said means.

8. In combination, an alternating current supply line, a transformer connected with said line, an electron discharge device connected with said transformer and having anodes with associated control electrodes and a cathode, a direct current output line connected with said transformer and with said device, means for rendering said control electrodes negative with respect to said cathode, inductive means in said output line, impedance means connected with said output line, means for bridging said inductive means with said impedance means, and means responsive to abnormal conditions in said output line to cause sequential operation of the third and fourth said means.

STEFAN WIDMER. 

